1. Field of the Invention
The present invention relates to an input device which is connected to a mobile communication terminal such as a mobile phone and with which characters can be input easily.
2. Description of the Related Art
In mobile terminals such as mobile phones and personal digital assistants (PDAs), characters are usually input by the following methods. In mobile phones, characters are input by using a numeric keypad (a group of keys including number keys and keys for the four basic operators). Japanese characters, for example, are input in the form of kana characters (Japanese syllabic alphabet, and there are two types: hiragana and katakana) or romaji (writing system based on Roman characters used to represent Japanese text). In PDAs, characters are input by writing each character on a liquid crystal display with a pen-type input device. In addition, keyboard-type input devices with a plurality of keys arranged thereon are sold separately, and are used for inputting characters by connecting them to the mobile terminals.
FIG. 6 is a perspective view of a known keyboard-type input device and a mobile terminal to which the keyboard-type input device is connected. With reference to FIG. 6, an input device 50 includes an operating unit 51 provided with a plurality of operation keys 52 and a connecting cable 53 which extends from the operating unit 51. The connecting cable 53 is provided with a connecter 54 at the distal end thereof, and the connecter 54 is attached to a connecting port 61 formed at the bottom end of a mobile terminal 60 in a detachable manner. The mobile terminal 60 includes an input unit 62 and a display unit 63.
In the input device 50, kana characters and romaji can be input by operating the operation keys 52. When the operation keys 52 are pressed, operating data is transmitted to the mobile terminal 60, and character strings are displayed on the display unit 63. Then, the character strings are converted into transmission data, which is transmitted from the mobile terminal 60 to other mobile terminals.
However, mobile terminals of the known art have the following problems.
When characters are input to a mobile phone without an input device connected thereto, a single key must be pressed up to five times in order to input a single hiragana character or katakana character, and a single key must be pressed up to three or four times in order to input a single alphabet character. Therefore, a relatively large input time is required. When characters are input to a PDA without an input device connected thereto, there is a problem in that characters are not recognized reliably. In addition, a large input time is also required in this case.
In the case in which the input device 50 shown in FIG. 6 is used, the operation to connect and disconnect the input device 50 to/from the mobile terminal is cumbersome. In addition, since the input device 50 and the mobile terminal 60 are connected to each other with the connecting cable, the user cannot input characters easily and smoothly while holding both the input device 50 and the mobile terminal 60. Furthermore, since the input device 50 must be disconnected from the mobile terminal 60 and carried separately when it is not being used, the input device 50 is not carried conveniently.